| << Chapter < Page | Chapter >> Page > |
| Listing 5 . The Comparator. |
|---|
class TheComparator implements Comparator,Serializable{
public int compare(Object o1,Object o2){if(!(o1 instanceof String))
throw new ClassCastException();if(!(o2 instanceof String))
throw new ClassCastException();int result = ((String)o1).compareTo(((String)o2));
return result*(-1);}//end compare()
}//end class TheComparator |
I have presented and explained this class in previous modules, so I won't discuss it in detail again here. Suffice it for now to say that an objectinstantiated from this class will induce the list to be sorted into reverse natural order .
The code in Listing 6 gets and uses an iterator to display the contents of the sorted list.
| Listing 6 . Display the sorted list. |
|---|
iter = ref.iterator();
while(iter.hasNext()){System.out.print(iter.next() + " ");
}//end while loop |
The output produced by the code in Listing 6 is shown below:
Tom TOM Joe JOE Bill BILL
As you can see, this is reverse natural order as induced by the Comparator object.
I encourage you to copy the code from Listing 1 . Paste the code into your Java editor. Thencompile and execute it.
Run the program and observe the results. Experiment with the code. Make changes, run the program again, and observe the results of your changes. Make certain that youcan explain why your changes behave as they do.
In this module, I taught you how to use the sort method of the Collections class along with a Comparator object to sort the contents of a list.
By using this approach, you can sort the contents of list according to any set of comparison rules that you can program into the compare method of the Comparator object.
Furthermore, the ability to sort the list is independent of the actual implementation of the list, so long as the list properly implements the List interface. For example, the same Comparator object (and the same code) can be used to sort an ArrayList , a LinkedList , or a Vector , producing the same results regardless of which class the list object isinstantiated from.
In the next module, I will show you how to use a Comparator created by the reverseOrder method of the Collections class to sort a list into reverse natural order . I will also show you how to use the reverse method of the Collections class to reverse the order of the elements in a list.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
-end-
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